Congenital hearing loss, which occurs once in every 500 births, is one of the most prevalent birth defects. One such hearing loss defect is the branchio-otio-renal syndrome (BOR), in which newborns have malformations in the external, middle and inner ear structures along with the presence of ear tags and pits. In 50% of BOR syndrome cases, mutations in the SIX1 or EYA1 gene are causative. The genetic etiology for the remaining 50% of BOR cases is not known, causing difficulty in accurate diagnosis. A timely and accurate detection of congenital hearing loss is shown to help direct appropriate therapy and prepare affected children and their families for managing progressive hearing loss. To address this knowledge gap, we aimed to first study how the proteome evolves as the inner ear develops. For this, we established a sensitive liquid chromatography (LC) – mass spectrometry (MS) approach to identify proteins from inner ears of the South African frog (Xenopus laevis) embryos and tadpoles. Since the frog inner ears are very similar to human and the embryo develops external to the mother, we were able to study the early stages of inner ear patterning. We used our LC-MS approach to quantify the relative abundance of proteins at five timepoints during the establishment of the inner ear, starting from a flattened disc (the otic vesicle) to the formation of the primary components of the inner ear. Our data revealed that the integrin pathway is statistically significantly overrepresented in the inner ear proteome. Moreover, most integrin pathway proteins were significantly more abundant in the established ear. Since many integrin pathway proteins such as collagen 2a and collagen 9 are associated with hearing loss syndromes, other detected pathway proteins could possibly be essential to ear development. We now plan to use our LC-MS approach to enhance our understanding of the BOR syndrome by assessing the effect of reducing the levels of Six1 on the inner ear proteome.
